Acoustical fiberboard and method of forming same



March 10, 1936. .1. N. DEVEREUX 2,033,124

ACCIUSTICAL FIBERBOARD AND METHOD OF FORMING SAME Filed Aug. 9, 1933 5/7765 Ar. fievereuzz,

Patented Man 10, 1936 UNITED STATES ACOUSTICAL FIBERBOARD AND METHOD OF FORMING SAME James N. Devereux, Greenville, Miss.

Application August 9, 1933, Serial No. 684,435

4 Claims.

My present invention relates generally to the manufacture of fiber board or fiber sheets of the type commonly used in the construction of buildings, in walls, roofs,- ceilings, partitions and wher- 5 ever fiber board is employed chiefly for its acoustical properties or sound absorption value, and my invention embraces not only the fiber board itself, but also the method by which it is formed.

In the manufacture of fiber board of the above type, it is customary to utilize wood, green or seasoned, cornstalks, or other vegetable fibers. In the formation of these fibers into a sheet, it is customary to make a thick mat, which by its thickness, is intended to impart the desired sound absorption quality to the board. The resulting mat is generally ofsuch heavy density, and the fine inter-connecting pores so clogged, that the acoustical value isgreatly impaired.

Some effort has been made to increase the sound absorption value of certain fiber board by cutting grooves, holes or other certain areas in the face of the board. Others have tried methods of covering the face of the board with paper and other similar material in order to produce thereby a diaphragm effect on the surface, and in this way increase the sound absorption of the product. These methods are costly and the resulting sound absorption value is not proportionately enhanced.

It is, of course, desirable to form the board on a single cylinder or wire machine, so that by a simple method, which is inexpensive, a fiber structure of such porosity and low density is secured, that the resulting product transforms a 35 great percentage of the incident sound energy into other forms of energy, and thereby demonstrates its unusual acoustical value.

The primary object of my invention is therefore, to provide'a fiber board which, by reason of its great number of fine inter-connecting pores, resulting from the unusual fiber structure and formation, insures a high coefiicient of sound absorption, as well as a method by which this desirable quality may be obtained.

' In the accompanying drawing, the single figure is a vertical sectional view through a forming cylinder and its vat, in connection with which my improved method is carried out.

In the manufacture of my improved fiber board, I preferably hydrate a watery mixture of short fine fibers and long'fine fibers and produce a suspension of these fibers, so that when the mixture is introduced into a vat, the short fine fibers are initially matted on the foraminous membrane of a forming cylinder thereof, into a thin sheet 5 about onefourth of the thickness of the finished sheet. This mat imparts the desired strength to the finished product and is relatively more hard and dense than the remaining thickness of the finished product.

The remaining long fibers are adhered to the above mat during the remainder of the opera.- tion, forming a loose, inter-laced fiber structure which embodies the fine, inter-connecting pores that are so particularly valuable to the sound absorption quality of the board.

In producing the above fibers several buhr stones are used for making fibers of different lengths and degrees of fineness, from logs or chips. In a preferred setting of the stones it has been found that the fineness of the stock from the stones will vary from about eight seconds to twelve seconds, and the composite stock will average around fourteen seconds, all as measured on a standard nine and one-half inch suction filter leaf having number twelve mesh. 'In use, cottonwood is preferred, but other woods, as willow, cypress, box elder, hackberry and the like, may be used.

The fiber, which is ground, is washed from the buhr stones, and mixed so that approximately three to five per cent of the fiber is either flour or ultra fine. The average length of the fibers in the mixture will be about three fourths of an inch, and the longest fibers will approximate one and one-half inches. This mixture of long and short, fine fibers is then screened to remove any pieces of 'wood or fibers longer thandesired and the screened stock is then watered and aerated and sizing materials, preferably consisting of a mix- 40 ture of rosin and alum, are added thereto. The rosin and alum react with one another and with the hardness in the water to produce complex bodies of an inorganic nature, portions of which rise to the surface of the stock mixture in the vat by reason of the flotation action of the foam produced by the agitation of the stock as it is fed into the vat.

Referring now to the drawing, a launder it conveys the diluted and mixed stock to the semlcircular vat ll, partially enclosing a; forming cylinder l2 which has a foraminous membrane I 3 around its periphery, and is operated under suction at from to five inches of suction or thereabouts, in order to facilitate the formation of a thick mat of fiber thereonand also to draw much of the water from the stock.

A plate 15 is provided adjacent to the discharge end or edge of the launder l 0, and is spaced therefrom to form substantially a feed slot l6, whereby the stock will be uniformly fed into the vat ll over the full width thereof and in this way produce a web I! having a substantially uniform thickness throughoutits width. In practice, this plate l5 preferably will be adjustable so that the widih of the feed slot I6 may be adjusted as desire The annular foraminous membrane l3 of the cylinder I2, is spaced from the wall of the vat H by a. space I 4 which continually decreases toward the discharge end of the vat, so that the I velocity of the stock is gradually increased to aid in keeping the fibers in suspension and enable more ready attraction of the fine fibers to the membrane l3 by the slight suction within the cylinder I 2, and the subsequent building up of the major portion of the body of the web of long, loosely inter-laced fibers before the web emerges from the surface of the stock within the vat II. It is extremely important that no'covering be upon this mass of loosely inter-laced fibers gathered naturally upon the previously formed and denser back mat of fine fibers. Therefore, while the rapid inflow of aerated and diluted stock from the launder It! causes the formation of foam which suspends therein considerable fine fibers,

and deposits some of these fibers along wit some of the sizing reaction products, when the foam is killed by water sprays l8, upon the board-sheet as it emerges from the vat, I subsequently remove this -deposit by the brushing action of a revolving brush l9, turning in a direction counter to the direction of rotation of the forming cylinder l2 after such deposit has served as a surface seal until the mat has been moved upwardly out of the water, so as to retain the water between the long loose body fibers. This brushing action removes all surface mat, levels ofi the sheet, and leaves exposed the long fibers and retained water which, by their position and structure, 'produce the high porosity and low density of the board for three quarters of the thickness thereof.

The fiber construction thus produced, is of such nature that, for the purposes of my invention and especially in its'wet condition, it should not be subjected to pressure, and therefore, the press rolls, usually employed to gradually press the web sheet to further remove water therefrom, are dispensed with and the web sheet conveyed directly to a suitable dryer. In my method the hydrating of the fibers does much to do away with the necessity for the usual press rolls, since it has been found that the drying action of the hot air in a standard fiber board dryer will, be-

cause of the unusual loosely interlaced structure Among the advantages of my improved fiber board as produced by the method above outlined, is its extremely low density, which makes it very light in weight and very easy to handle in use.

The following table gives a list of tests made on samples ofthis fiber board, showing the sound absorption value based on the coefficient of sound.

absorption method listed in the reports of the Bureau of Standards on this subject, as compared to the density of the board.

04 soundab- Density sorption copounds'cubic efficient feet It can be readily seen. from the foregoing that there is a generally fair agreement between the density of the board and its coefficient of sound absorption, although it is to be understood that I do not limit my invention to such agreement, nor in fact to anything not specifically stated as limiting the invention, and I reserve all modifications and equivalents within the spirit therelating the long fibers in loose natural adherence with one another in the water of the mixtureand -with said back mat to form the major portion of the thickness of the board, then depositing short fibers on the loose body fibersto seal its surface, subsequently removing said fibrous surface seal, and then drying the same without pressureto remove the excess moisture thereof.

2. The method of forming an acoustical fiber board, which consists in utilizing hydrated long and short fibers in a watery mixture, first felting the short fibers in said mixture to form a strengthening back mat, then accumulating the long fibers in the mixture in natural adherence with one another and with said back mat to form the major portion of the thickness of the board, brushing the surface of the board to remove surface short fibers, and then, without applying pressure to remove excess moisture, drying the fibers so felted and accumulated.

3. The method of forming a homogeneous acoustical fiber board, which consists in utilizing hydrated long and short fibers in a watery mixture, first felting the short fibers in the mixture to form a strengthening back for the mat, then accumulating the long fibers in natural adherence with one another in the water of the mixture and on said mat back, sealing the surface of the accumulated long fibers to hold the water filling the interstices thereof until the mat has been moved out of the forming mixture, then. removing the said sealing surface in order to expose the loose porous body of long fibers, and then drying the mat without pressure to effect removal of the excess without disturbing the porous nature of the loose fiber structure of the board.

4. The method of forming a homogeneous acoustical fiber board which consists in utilizing long and short fibers in a watery mixture, felting the short fibers in a strengthening back for the mat, accumulating the long fibers in a loose mat on said back having the interstices thereof filled with water, sealing the surface of the mat to retain the water therein until the mat has been moved out of the forming mixture, then removing the sealing surface to expose the water and long fibers of the mat, and then drying the mat to remove the water and leave the loose fiber structure intact without a collapse of the fibers 5 due to the loss of the water.

JAMES N. DEVEREUX. 

